Photocatalytic water splitting has been studied as a way to harness solar energy by using it to generate clean, high energy-containing hydrogen from water, an abundant, inexpensive feedstock. Efforts have been directed toward producing compounds with higher catalytic activity in the photolysis of water. Catalytic activity of the titanium dioxide-based photocatalysts originally studied was improved with catalysts such as Pt/TiO2 and RuO2/TiO2. Strontium-titanium oxide-based materials such as a reduced SrTiO3/platinum electrode pair, SrTiO3 powder modified with rhodium oxide, platinized SrTiO3, and nickel-loaded SrTiO3 have been studied, but the amount of absorbed photons used in the photolysis for these photocatalysts (the “quantum yield”) is less than 1%. More recently, quantum yields of 5-10% have been obtained with layered structures of K4Nb6O17, K4TaxNb6-xO17, and Rb4TaxNb6-xO17, and quantum yields as high as 30% have been obtained with K2La2Ti3O10 prepared in a polymerized complex method. The materials with improved quantum yield have interlayer reaction sites that can physically separate electron and hole pairs created by photoabsorption to retard electron-hole recombination. Even higher photocatalytic activity of the complex oxides would be desirable, however.
One reference concerning photocatalytic properties and electronic structure of lanthanide tantalates, teaches preparing lanthanide tantalates by calcining powder mixtures of lanthanum oxides with tantalum oxide at 1200° C. (1473K) for 10 hours in air. The as-prepared calcined powder precursor is impregnated with aqueous nickel nitrate and submitted to reduction in hydrogen at 500° C., then oxidation in oxygen at 200° C. to provide a nickel-loaded catalyst with partially oxidized nickel. The authors reported a photocatalytic activity of LaTaO4 loaded with 0.7 wt % of Ni using 200 cc water and 0.2 g catalyst of 115.6 μmol hydrogen/hr. and 51.5 μmol oxygen/hr.
It is desirable to have the catalytic activity as high as possible to capture more energy-rich hydrogen fuel. Thus, a need remains increasing the catalytic activity of photocatalytically active materials.